Debt Disclosure [Abstract] Credit Facility [Table] Line of Credit Facility [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Term Loan Secured Debt [Member] Uncommited Line Uncommitted Line of Credit [Member] Uncommitted Line of Credit Credit Facility [Line Items] Line of Credit Facility [Line Items] Credit facility, term Debt Instrument, Term Credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Credit facility, commitment fee rate Line of Credit Facility, Commitment Fee Percentage Credit facility borrowings Long-term Line of Credit Weighted average interest during period Debt, Weighted Average Interest Rate Increase (decrease) in lines of credit Line of Credit Facility, Maximum Borrowing Capacity, Period Increase (Decrease) Line of Credit Facility, Maximum Borrowing Capacity, Period Increase (Decrease) Proceeds from lines of credit Proceeds from Issuance of Debt Insurance [Abstract] Statutory Accounting Statutory Accounting Disclosure [Text Block] Represents the entire disclosure pertaining to the statutory accounting. Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Summary of nonvested Common Share and nonvested Common Share unit activity Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Schedule of portion of nonvested Common Shares earned based upon achievement of compounded annual book value per share growth Schedule of Shares Earned Unvested Performance Shares [Table Text Block] Tabular disclosure of shares earned for unvested performance shares. Schedule of compensation expense, net of forfeitures, and related tax effects recognized in connection with nonvested shares Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Investments, Debt and Equity Securities [Abstract] Schedule of investments available for sale Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Schedule of amortized cost and fair value of investments available for sale by contractual maturity Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of realized gross gains and losses on sale of investments available for sale Schedule of Realized Gain (Loss) [Table Text Block] Schedule of fair value of investments in an unrealized loss position and related unrealized losses Schedule of Unrealized Loss on Investments [Table Text Block] Schedule of net investment income Investment Income [Table Text Block] Document and Entity Information Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Earnings Per Share [Abstract] Schedule of reconciliation of net income and weighted average common shares outstanding used in computations of basic and diluted earnings per common share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Fair Value Disclosures [Abstract] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Investment Issuer [Axis] Investment Issuer [Axis] Investment Issuer [Domain] Investment Issuer [Domain] U.S. Agency US Government Corporations and Agencies Securities [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] U.S. Treasury securities US Treasury Securities [Member] U.S. agency securities US Government Agencies Debt Securities [Member] Municipal debt securities Municipal Bonds [Member] Corporate debt securities Corporate Debt Securities [Member] U.S. agency mortgage-backed securities Collateralized Mortgage Backed Securities [Member] Residential and commercial mortgage securities Residential And Commercial Mortgage Securities [Member] Residential And Commercial Mortgage Securities [Member] Asset-backed securities Asset-backed Securities [Member] Money market funds Money Market Funds [Member] Investments available for sale Schedule of Available-for-sale Securities [Line Items] Amortized Cost Available-for-sale Securities, Amortized Cost Basis [Abstract] Due in 1 year Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Amortized Cost Basis Due after 1 but within 5 years Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis Due after 5 but within 10 years Available-for-sale Securities, Debt Maturities, Rolling Year Six Through Ten, Amortized Cost Basis Due after 10 years Available-for-sale Securities, Debt Maturities, Rolling after Year Ten, Amortized Cost Basis Subtotal Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Amortized Cost Available-for-sale Securities, Amortized Cost Basis Fair Value Available-for-sale Securities [Abstract] Due in 1 year Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Fair Value Due after 1 but within 5 years Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value Due after 5 but within 10 years Available-for-sale Securities, Debt Maturities, Rolling Year Six Through Ten, Fair Value Due after 10 years Available-for-sale Securities, Debt Maturities, Rolling after Year Ten, Fair Value Subtotal Available-for-sale Securities, Debt Maturities, Single Maturity Date Total investments Available-for-sale Securities Net income Net Income (Loss) Attributable to Parent Less: dividends declared Dividends Net income Net Income (Loss) Available to Common Stockholders, Basic Basic earnings per share (in dollars per share) Earnings Per Share, Basic Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Basic weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Dilutive effect of nonvested shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Diluted weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Statement of Cash Flows [Abstract] Operating Activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Gain on the sale of investments, net Realized Investment Gains (Losses) Depreciation and amortization Depreciation, Depletion and Amortization Stock-based compensation expense Share-based Compensation Amortization of premium on investment securities Investment Income, Amortization of Premium Deferred income tax provision Deferred Income Tax Expense (Benefit) Change in: Increase (Decrease) in Operating Capital [Abstract] Accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Accounts receivable Increase (Decrease) in Accounts Receivable Deferred policy acquisition costs Increase (Decrease) in Deferred Policy Acquisition Costs Prepaid federal income tax Increase (Decrease) in Mortgage Guaranty Insurer United States Mortgage Guaranty Tax and Loss Bonds Represents, for a mortgage guaranty insurer, the increase (decrease) during the reporting period in the amount of investment in United States Mortgage Guaranty Tax and Loss Bonds issued by the Treasury Department for eligibility for certain tax deductions under enacted tax laws. Other assets Increase (Decrease) in Other Operating Assets Reserve for losses and LAE Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Unearned premium reserve Increase (Decrease) in Unearned Premiums Other accrued liabilities Increase (Decrease) in Accrued Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Net change in short-term investments Payments for (Proceeds from) Short-term Investments Purchase of investments available for sale Payments to Acquire Available-for-sale Securities Proceeds from maturity of investments available for sale Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Proceeds from sales of investments available for sale Proceeds from Sale of Available-for-sale Securities Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing Activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Credit facility borrowings Proceeds from Long-term Lines of Credit Treasury stock acquired Payments for Repurchase of Common Stock Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Net decrease in cash Cash and Cash Equivalents, Period Increase (Decrease) Cash at beginning of year Cash and Cash Equivalents, at Carrying Value Cash at end of period Supplemental Disclosure of Cash Flow Information Supplemental Cash Flow Information [Abstract] Income tax payments Income Taxes Paid, Net Interest payments Interest Paid Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Indemnifications related to contract underwriting services Indemnification Agreement [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Amount paid for remedies (less than) Loss Contingency Accrual, Payments Residential and commercial mortgage securities Amortized Cost Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Fair Value Debt Obligations Debt Disclosure [Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Nonvested shares Restricted Stock [Member] Stock-based compensation Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Total fair value of shares vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Total unrecognized compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options Expected weighted average period for recognition of expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Shares tendered by employees to pay employee withholding taxes (in shares) Shares Paid for Tax Withholding for Share Based Compensation Compensation expense, net of forfeitures, and related tax effects recognized in connection with nonvested shares Share-based Compensation, Allocation and Classification in Financial Statements [Abstract] Compensation expense Allocated Share-based Compensation Expense Income tax benefit Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] First Vesting Period Share-based Compensation Award, Tranche One [Member] Second Vesting Period Share-based Compensation Award, Tranche Two [Member] Third Vesting Period Share-based Compensation Award, Tranche Three [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2013 Plan Essent Group Limited2013 Long Term Incentive Plan [Member] Represents the Essent Group Limited 2013 Long-term Incentive Plan (2013 Plan). Vesting Criteria [Axis] Vesting Criteria [Axis] Information about the type of vesting for share-based compensation awards. Vesting Criteria [Domain] Vesting Criteria [Domain] The types of vesting specified for share-based compensation awards. Time-Based Vesting Based On Service [Member] Represents a share based compensation award with vesting based on length of service. Performance -Based Vesting Based On Performance [Member] Represents a share based compensation award with vesting based on achievement of performance conditions. Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Certain members of senior management Certain Senior Management [Member] Represents some, but not all, of a team of individuals at the highest level of organizational management who have the day-to-day responsibilities of managing the entity. Performance period Share Based Compensation Arrangement by Share Based Payment Award Performance Period Represents the period over which a performance condition to the award is measured, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Vesting (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Fixed maturities Fixed Maturities [Member] Short-term investments Short-term Investments [Member] Statement Statement [Line Items] Investments available for sale Amortized cost Property and equipment Property, Plant and Equipment, Net [Abstract] Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Credit Facility Borrowings Subordinated Borrowings [Abstract] Unamortized deferred costs Debt Issuance Costs, Gross Stockholders’ Equity Stockholders' Equity Attributable to Parent [Abstract] Common Shares, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common Shares, authorized (in shares) Common Stock, Shares Authorized Common Shares, issued (in shares) Common Stock, Shares, Issued Common Shares, outstanding (in shares) Common Stock, Shares, Outstanding Schedule of assets and liabilities measured at fair vale on a recurring basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Investment Income [Table] Investment Income [Table] Components of net investment income Net Investment Income [Line Items] Gross investment income Gross Investment Income, Operating Investment expenses Investment Income, Investment Expense Net investment income Net Investment Income Statutory Accounting Practices [Table] Statutory Accounting Practices [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Essent Guaranty Essent Guaranty Inc [Member] Represents information pertaining to Essent Guaranty, Inc. (Essent Guaranty), a regulated and licensed indirect wholly-owned subsidiary of the reporting entity. Essent PA Essent PA [Member] Essent PA [Member] Essent Re Essent Reinsurance Ltd [Member] Represents information pertaining to Essent Reinsurance Ltd. (Essent Re), a wholly-owned Bermuda-domiciled Class 3A Insurer licensed pursuant to Section 4 of the Bermuda Insurance Act 1978, which offers mortgage-related insurance and reinsurance. Dividends Restrictions Statutory Accounting Practices [Line Items] Statutory net income Statutory Accounting Practices, Statutory Net Income Amount Statutory surplus Statutory Accounting Practices, Statutory Surplus Balance Represents the amount of statutory surplus (stockholders' equity), as of the balance sheet date, using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country. Contingency reserve liability Statutory Accounting Practices, Statutory Contingency Reserve Liability Represents the amount of contingency reserve liability, as of the balance sheet date, using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country. Increase in contingency reserve Statutory Accounting Practices, Increase (Decrease) in Contingency Reserve Represents the amount of increase (decrease) in contingency reserve. Statutory capital and surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance Reinsurance Disclosures [Abstract] Reinsurance Reinsurance [Text Block] Time and Performance- Based Share Awards Vesting Based On Service And Performance [Member] Represents a share based compensation award with vesting based on a combination of length of service and achievement of performance conditions. Time-Based Share Awards Nonvested share units Restricted Stock Units (RSUs) [Member] Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Outstanding at beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding at end of period (in shares) Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Outstanding at beginning of year (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Outstanding at end of period (in dollars per share) Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Employee Employee [Member] Employee [Member] Director Director [Member] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] Incentive Program Bonus Award Fiscal Year Performance Incentive Program Bonus Award Fiscal Year Performance [Member] Represents an incentive program covering bonus awards based on performance for previous fiscal year. Award vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Accounting Policies [Abstract] Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Assets Assets [Abstract] Investments available for sale, at fair value Fixed maturities (amortized cost: 2018 — $2,116,143; 2017 — $1,994,200) Marketable Securities, Fixed Maturities Short-term investments (amortized cost: 2018 — $380,776; 2017 — $312,714) Short-term Investments Total investments Investments Cash Cash Accrued investment income Accrued Investment Income Receivable Accounts receivable Accounts Receivable, Net Deferred policy acquisition costs Deferred Policy Acquisition Costs Property and equipment (at cost, less accumulated depreciation of $51,363 in 2018 and $50,466 in 2017) Property, Plant and Equipment, Net Prepaid federal income tax Mortgage Guaranty Insurer United States Mortgage Guaranty Tax and Loss Bonds Represents, for a mortgage guaranty insurer, the amount of investment in United States Mortgage Guaranty Tax and Loss Bonds issued by the Treasury Department for eligibility for certain tax deductions under enacted tax laws. Other assets Other Assets Total assets Assets Liabilities and Stockholders’ Equity Liabilities and Equity [Abstract] Liabilities Liabilities [Abstract] Reserve for losses and LAE Liability for Unpaid Claims and Claims Adjustment Expense, Net Unearned premium reserve Unearned Premiums Net deferred tax liability Deferred Tax Liabilities, Net Credit facility borrowings (at carrying value, less unamortized deferred costs of $1,303 in 2018 and $1,409 in 2017) Securities purchases payable Investment-related Liabilities Other accrued liabilities Other Accrued Liabilities Total liabilities Liabilities Commitments and contingencies (see Note 7) Commitments and Contingencies Stockholders’ Equity Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract] Common shares, $0.015 par value: Authorized - 233,333; issued and outstanding - 98,102 shares in 2018 and 98,434 shares in 2017 Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total stockholders’ equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders’ equity Liabilities and Equity Recently Issued Accounting Standards Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract] Reconciliation of the beginning and ending reserve balances for losses and loss adjustment expenses (LAE) Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Reserve for losses and LAE at beginning of period Liability for Claims and Claims Adjustment Expense Less: Reinsurance recoverables Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Net reserve for losses and LAE at beginning of period Add provision for losses and LAE, net of reinsurance, occurring in: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current period Current Year Claims and Claims Adjustment Expense Prior years Prior Year Claims and Claims Adjustment Expense Net incurred losses and LAE during the current period Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Deduct payments for losses and LAE, net of reinsurance, occurring in: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current period Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Net loss and LAE payments during the current period Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Net reserve for losses and LAE at end of period Plus: Reinsurance recoverables Reserve for losses and LAE at end of period Loans in default at end of period Number of Loans in Default Represents the number of loans in default. Organization, Consolidation and Presentation of Financial Statements [Abstract] Nature of Operations and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Affiliated Entity Affiliated Entity [Member] Essent PA Essent Guaranty Of P A Inc [Member] Represents information pertaining to Essent Guaranty of PA, Inc. (Essent PA), a regulated and licensed indirect wholly-owned subsidiary of the reporting entity. Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Quota share reinsurance Quota Share Reinsurance Transaction [Member] Represents an agreement between an insurer and a reinsurer whereby the reinsurer pays an agreed-upon percentage of all losses the insurer sustains. Reinsurance for mortgage insurance coverage in excess of 25% Excess Mortgage Insurance Coverage [Member] Represents an arrangement to assume that portion of the risk retained by an affiliate that is in excess of 25% of the balance of any mortgage loan insured by that affiliate after consideration of other reinsurance agreements at that affiliate, in accordance with certain state law requirements. Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Residential mortgage down payment percentage for which mortgage insurance is generally required (less than) Loans and Leases Receivable Consumer Mortgage Insured Down Payment Percentage Represents the percentage of the total sale price that a home buyer contributes in cash towards the purchase of a home for which mortgage insurance is generally required. Number of states in which the entity is licensed to write mortgage insurance Number of States in which Entity Operates Reinsurance percentage Reinsurance Retention Policy, Reinsured Risk, Percentage Reinsurance for mortgage insurance coverage threshold (in excess of) Reinsurance Retention Policy, Reinsured Risk, Percentage Threshold Threshold percentage of risk reinsured on insurance products per entity policy. Investments Available for Sale Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Change in unrealized appreciation (depreciation) of investments, tax expense (benefit) Other Comprehensive Income (Loss), Available-for-sale Securities, Tax, Portion Attributable to Parent Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Accumulated Net Investment Gains (Losses) On Investments Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Before Tax AOCI Attributable To Parent, Before Tax [Roll Forward] AOCI Attributable To Parent, Before Tax [Roll Forward] AOCI before tax, beginning of period AOCI before Tax, Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent [Abstract] Unrealized holding gains (losses) arising during the period, before tax OCI, before Reclassifications, before Tax, Attributable to Parent Less: Reclassification adjustment for gains included in net income, before tax Reclassification from AOCI, Current Period, before Tax, Attributable to Parent Other comprehensive income (loss), before tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent AOCI before tax, end of period Tax Effect AOCI Attributable To Parent, Tax [Roll Forward] AOCI Attributable To Parent, Tax AOCI tax effect, beginning of period AOCI Tax, Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent, Parenthetical Disclosures [Abstract] Unrealized holding (gains) losses arising during the period, tax effect Other Comprehensive Income (Loss) before Reclassifications, Tax Less: Reclassification adjustment for gains included in net income, tax effect Reclassification from AOCI, Current Period, Tax Other comprehensive (income) loss, tax effect Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent AOCI tax effect, end of period Net of Tax AOCI Attributable to Parent, Net of Tax [Roll Forward] Stockholders equity, beginning of period Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized holding gains (losses) arising during the period, net of tax OCI, before Reclassifications, Net of Tax, Attributable to Parent Less: Reclassification adjustment for gains included in net income, net of tax Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Total other comprehensive (loss) income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Stockholders equity, end of period Effect of reinsurance Effects of Reinsurance [Table Text Block] Schedule of VIE assets and maximum exposure Schedule of Variable Interest Entities [Table Text Block] Reinsurance Premiums for Insurance Companies, by Product Segment [Table] Reinsurance Premiums for Insurance Companies, by Product Segment [Table] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Radnor Re Radnor Re 2018-1 Ltd. [Member] Radnor Re 2018-1 Ltd. Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Mortgage Insurance Linked Notes Mortgage Insurance Linked Notes [Member] Mortgage Insurance Linked Notes [Member] Reinsurance Policy, Type [Axis] Reinsurance Policy, Type [Axis] Reinsurance Policy [Domain] Reinsurance Policy [Domain] Mortgage Insurance Mortgage Insurance [Member] Mortgage Insurance [Member] Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items] Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items] Aggregate reinsurance agreement Reinsurance Retention Policy, Excess Retention, Amount Reinsured First layer retention Variable Interest Entity First Layer Retention Variable Interest Entity First Layer Retention Amortization period Amortization Period Excess of Loss Portfolio Amortization Period Excess of Loss Portfolio Option to terminate, commencement period Reinsurance Retention Policy, Option To Terminate, Period Reinsurance Retention Policy, Option To Terminate, Period Ceded premium payable increase, percent Risk Margin Component Of Reinsurance Premium Payable, Percent Risk Margin Component Of Reinsurance Premium Payable, Percent Debt amount Debt Instrument, Face Amount Maturity Reinsurance Retention Policy, Debt Issued To Cover Insurance, Term Reinsurance Retention Policy, Debt Issued To Cover Insurance, Term Statement of Stockholders' Equity [Abstract] Common Shares Common Stock [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Treasury Stock Treasury Stock [Member] Changes in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Net income Other comprehensive income (loss) Issuance of common shares, net of issuance cost of $1,802 Stock Issued During Period, Value, New Issues Issuance of management incentive shares Stock Issued During Period, Value, Share-based Compensation, Gross Stock-based compensation expense Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Cumulative effect of ASU 2016-09 adoption Cumulative Effect of New Accounting Principle in Period of Adoption Treasury stock acquired Treasury Stock, Value, Acquired, Cost Method Cancellation of treasury stock Treasury Stock, Retired, Cost Method, Amount Reclassification of certain income tax effects resulting from tax reform Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings Tax Cuts And Jobs Act of 2017, Reclassification From AOCI To Retained Earnings Compounded Annual Book Value Per Share Growth 15% Compounded Annual Book Value Per Share Growth Achieved 15 Percent [Member] Represents information pertaining to 15% compounded annual book value per share growth achieved. Compounded Annual Book Value Per Share Growth 16% Compounded Annual Book Value Per Share Growth Achieved 16 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 16 Percent [Member] Compounded Annual Book Value Per Share Growth 17% Compounded Annual Book Value Per Share Growth Achieved 17 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 17 Percent [Member] Compounded Annual Book Value Per Share Growth 18% Compounded Annual Book Value Per Share Growth Achieved 18 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 18 Percent [Member] Minimum Minimum [Member] Compounded Annual Book Value Per Share Growth Compounded Annual Book Value Per Share Growth Rate Represents the compounded annual book value per share growth rate, expressed as a percentage. Nonvested Common Shares Earned Revenues: Revenues [Abstract] Net premiums written Premiums Written, Net Increase in unearned premiums (Increase) Decrease in Unearned Premiums, Net Net premiums earned Premiums Earned, Net Net investment income Realized investment gains, net Other income Other Income Total revenues Revenues Losses and expenses: Benefits, Losses and Expenses [Abstract] Provision for losses and LAE Other underwriting and operating expenses Other Underwriting and Operating Expenses Represents the aggregate amount of costs incurred during the period, such as those relating to general administration and policy maintenance that do not vary with, and are not primarily related to the acquisition or renewal of insurance contracts and other operating costs, that are associated with the entity's normal revenue producing operation. Interest expense Interest Expense Total losses and expenses Benefits, Losses and Expenses Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Earnings per share: Earnings Per Share, Basic and Diluted [Abstract] Basic (in dollars per share) Diluted (in dollars per share) Weighted average shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Diluted (in shares) Other comprehensive income (loss): Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Change in unrealized (depreciation) appreciation of investments, net of tax (benefit) expense of ($5,193) in 2018 and $2,061 in 2017 Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Net premiums written: Premiums Written, Net [Abstract] Direct Direct Premiums Written Ceded Ceded Premiums Written Net premiums written Net premiums earned: Premiums Earned, Net [Abstract] Direct Direct Premiums Earned Ceded Ceded Premiums Earned Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] Public Offering Secondary Offering [Member] Secondary Offering [Member] Common stock, issuance cost Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Performance-based share awards Performance Shares [Member] EPS calculation Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Contingently issuable awards Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Antidilutive nonvested shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Percentage of award issuable if current period end were end of contingency period Share-based Compensation Arrangement by Share-based Payment Award, Award Period to Date Vesting Rights, Percentage Percentage of vesting of share-based compensation awards if the end of the current reporting period were the end of the vesting period. Investment Secondary Categorization [Axis] Investment Secondary Categorization [Axis] Investments by Secondary Categorization [Domain] Investments by Secondary Categorization [Domain] Special revenue bonds Special Revenue Municipal Bonds [Member] A municipal bond whose debt service is payable solely from the revenues derived from operating the facilities acquired or constructed with the proceeds of the bonds. General obligation bonds General Obligation Municipal Bonds [Member] A bond secured by a pledge of the issuer's taxing powers (limited or unlimited). More commonly the general obligation bonds of local governments are paid from ad valorem property taxes and other general revenues. Considered the most secure of all municipal debt. Certificate of participation bonds Certification Of Participation Bonds [Member] Represents a type of financing where an investor purchases a share of the lease revenues of a program rather than the bond being secured by those revenues. Tax allocation bonds Tax Allocation Municipal Bonds [Member] Bonds issued in conjunction with a redevelopment project. The taxes pledged to their repayment come from the increase of assessed value over and above a pre-established base. The redevelopment creates this added value, known as the tax increment. Special tax bonds Special Tax Bond [Member] Special Tax Bond [Member] Investment Sector [Axis] Investment Sector [Axis] Investment Sector [Domain] Investment Sector [Domain] Financial Financial Sector [Member] Financial Sector [Member] Consumer, non-cyclical Consumer, Non-cyclical Sector [Member] Consumer, Non-cyclical Sector [Member] Communications Communications Sector [Member] Communications Sector [Member] Energy Energy Sector [Member] Energy Sector [Member] Utilities Utilities Sector [Member] Utilities Sector [Member] Industrial Industrial Sector [Member] Industrial Sector [Member] Consumer, cyclical Consumer, Cyclical Sector [Member] Consumer, Cyclical Sector [Member] Technology Technology Debt Sector [Member] Technology Debt Sector [Member] Basic materials Basic Materials Sector [Member] Basic Materials Sector [Member] Percentage of debt securities Investment Owned, Percent of Net Assets Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Rollforward of accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Total VIE Assets Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets Maximum Exposure to Loss, On - Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount On The Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount On The Balance Sheet Maximum Exposure to Loss, Off - Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Off The Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Off The Balance Sheet Maximum Exposure to Loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Earnings per Share (EPS) Earnings Per Share [Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Quoted Prices in Active Markets for Identical Instruments (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring basis Fair Value, Measurements, Recurring [Member] Estimated fair values and carrying amounts of financial instruments Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial Assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Total assets at fair value Assets, Fair Value Disclosure Schedule of reconciliation of beginning and ending reserve balances for losses and loss adjustment expenses (LAE) Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Reserve for Losses and Loss Adjustment Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Schedule of statutory net income, statutory surplus and contingency reserve liability Statutory Accounting Practices Disclosure [Table Text Block] Realized gross gains and losses on the sale of investments available for sale Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract] Realized gross gains Available-for-sale Securities, Gross Realized Gains Realized gross losses Available-for-sale Securities, Gross Realized Losses Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] Less than 12 months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 12 months or more Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Total Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract] Less than 12 months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 12 months or more Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Total Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Other information Available-for-sale Securities, Other Disclosure Items [Abstract] Other-than-temporary impairments Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Fair value of investments deposited with insurance regulatory authorities Available-for-sale Securities, Restricted Fair value of the required investments on deposit in trusts Assets Held-in-trust Deposits assets Assets On Deposit For The Benefit Of The Reinsurer Assets On Deposit For The Benefit Of The Reinsurer Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Catastrophic Event [Axis] Catastrophic Event [Axis] Catastrophic Event [Domain] Catastrophic Event [Domain] Hurricane Hurricane [Member] Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Number of loans in hurricane impacted areas in default Number Of Loans In Hurricane Impacted Areas In Default Number Of Loans In Hurricane Impacted Areas In Default Number of loans in hurricane impacted areas in default cured during period Number Of Loans In Hurricane Impacted Areas In Default Cured During Period Number Of Loans In Hurricane Impacted Areas In Default Cured During Period Liability for claims and claims adjustment expense Incurred claims and claim adjustment expenses Favorable prior year development Reserve for losses and LAE, for prior years Liability for Unpaid Claims and Claims Adjustment Expense Prior Years Liability, as of the balance sheet date, for amounts representing estimated cost of settling unpaid claims for prior years under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims.